This invention relates to a magnetoresistive effect element, magnetic head and magnetic recording apparatus, and more particularly, to a magnetoresistive effect element structured to flow a sense current vertically of the film surface of a magnetoresistive effect film, as well as a magnetic head and a magnetic reproducing apparatus using the magnetoresistive effect element.
Following to the discovery of giant magnetoresistive effects (GMR) in multi-layered structures of magnetic layers, there is an epoch-making progress in performance of magnetic devices, especially of magnetic heads. Especially, discovery of GMR by spin-valve (SV) films brought about a large technical progress in the field of magnetic devices.
A spin-valve film is a multi-layered film made by interposing a nonmagnetic layer between two metal ferromagnetic films, in which magnetization of only one ferromagnetic layer (called “pinned layer” or “magnetization-pinned layer”) is fixed in one direction by a bias magnetic field from an antiferromagnetic layer or hard-magnetic layer whereas magnetization of the other ferromagnetic layer (called “free layer” or “magnetization free layer”) varies in direction in response to an external magnetic head to make a relative angle with respect to the pinned layer, thereby to exhibit a giant magnetoresistance change.
Regarding this kind of spin valve films, those used in CPP (current perpendicular to plane) type magnetoresistive effect elements configured to supply a sense current substantially perpendicularly to the film plane exercise larger giant magneto resistive effects than those used in CIP (current in plane) type magnetoresistive effect elements configured to supply a sense current in parallel to the film plane.
As one type of CPP type magnetoresistive effect elements, TMR elements making use of tunneling magnetoresistive effect (TMR) have also been developed. TMR elements, however, are characterized in the use of an insulating layer of alumina, for example, as the intervening nonmagnetic layer, and accordingly, there is a difference also in the mechanism of the device operation.
In addition to giving a larger magnetoresistive variable rate that that of a CIP magnetoresistive effect element, a CPP magnetoresistive effect element additionally has the advantage that the resistance variable amount increases when the device is downsized because the resistance of the element depends on the device area. This advantage is more significant today where magnetic devices are progressively downsized. Therefore, magnetic CPP magnetoresistive effect elements and magnetic heads using them will be hopeful candidates for realization of a recording density not lower than 100 gigabits per square inch (100 Gbpsi).
However, in case of TMR elements, the insulator used as the intermediate layer excessively increase the device resistance, and it is its difficulty that downsizing of the device area causes shot noise peculiar to the tunneling phenomenon due to a large resistance, or deterioration of the response to high frequencies.
On the other hand, in case of CPP elements using a metal nonmagnetic intermediate layer and having a much smaller device resistance than TMR elements, when a sense current is supplied perpendicularly to the film plane, the resistance variable amount itself is significantly small even though the resistance variable rate is gigantic. As a result, it is difficult to obtain a large reproduction output signal.
For the purpose of overcoming this problem, there is a report on a method of increasing the resistance and obtaining a large change of resistance by stacking an extremely thin oxide layer on a CPP element using a metal nonmagnetic intermediate layer (K. Nagasaka et al; The 8th Joint MMM-Intermag. Conference, DD-10). In this method, it is attempted to obtain a high resistance by locally forming a metal-like low-resistance region like a pinhole in an oxide layer and confining a current thereby. However, it is difficult to form uniform pinholes. Thus, it is a hurdle against its practical use that the resistance largely varies when the recording density increases to or beyond 100 Gbpsi, where the device size is in the order of 0.1 μm, and uniform CPP elements are difficult to manufacture.